The present invention is directed to an integrated global aircraft surveillance and navigation system having capabilities beyond those of the system described in U.S. Pat. No. 4,454,510 which issued Jul. 12, 1984 in the name of the present inventor. That patent discloses an aircraft surveillance, navigation, landing guidance and collision avoidance system which takes the form of a two-way data communication link between each of a multiplicity of controlled aircraft and a ground station. The system described in the patent also includes appropriate measuring equipment at the ground station which provides three-dimensional position data on the ground for aircraft control purposes, and which also provides three-dimensional position data in the aircraft for navigation, landing guidance and collision avoidance purposes. A two-way air/ground data link is also provided for miscellaneous data and control purposes.
Specifically, the present invention is concerned with a combined ground and satellite system for providing precise global aircraft navigation, surveillance, landing guidance, collision avoidance, and data linkage with a ground-based system, and which has capabilities beyond those of present day Global Positioning Systems (GPS).
Global civil aviation is rapidly moving toward widespread utilization of the prior art military Global Positioning System (GPS) and the civil version Global Navigation Satellite System (GNSS) yet to be implemented, both of which have substantial navigation advantages over previous systems. However, although the GPS-based landing guidance and dependent surveillance systems offer major advantages over the previously existing systems, there are critical shortcomings in present day GPS systems which involve integrity, availability and security. These shortcomings cannot practically be solved with the GPS-based systems or with the GNSS-based systems. In the GPS-dependent surveillance system, aircraft-derived GPS position data is transmitted to the ground by way of a constellation of communications satellites. It has been found that a constellation of eight geo-stationary and polar-orbiting satellites are sufficient to provide global coverage with redundancy in case of a satellite outage. A GPS-equipped aircraft may be interrogated by an Air Traffic Control (ATC) ground facility by way of one of the communications satellites, utilizing a discrete address, and the aircraft then replies by sending data representing its latitude/longitude, altitude and miscellaneous details using the same satellite link. Therefore, aircraft three-dimensional position data is made available to the Air Traffic Control (ATC) regardless of where the aircraft is located with respect to the earth.
Once the GPS communications satellite constellation referred to above is established for surveillance, means for global collision warning/avoidance is also available. The addition of a receiver on board the aircraft which operates on the aircraft-to-satellite up-link frequency enables all the aircraft in the vicinity to receive three-dimensional position data. This data can be processed for traffic environment display and horizontal, as well as vertical, escape maneuvers.
Although the GPS-based global functions such as those listed above represent distinct advances over the previously-used systems, there are many reasons for civil aviation to advance beyond GPS or GNSS-based systems. Some of these reasons are as follows:
A. The GPS-dependent global surveillance depends on accurate GPS positions from all aircraft. If there is a positional error from one aircraft, for whatever reason, a potential conflict with other aircraft in the vicinity arises which could lead to disaster. On the other hand, position data for a number of aircraft in an area derived from a common ground or satellite source, as is the case in the system of the present invention, is not subject to such a disastrous result.
B. The collision warning/avoidance function available in the GPS is superior to existing Threat Collision Avoidance Systems (TCAS) in that accurate relative positions are known in the GPS system of each aircraft, enabling cockpit traffic environment display, and horizontal as well as vertical escapes to be made. But this is also subject to the problem discussed in the previous paragraph, that is, the problem of potential aircraft conflicts if one aircraft reports an erroneously derived GPS position.
C. Although differential GPS-based landing guidance appears to be attractive from many aspects, it falls short in at least required integrity and availability with respect to existing Instrument Landing System (ILS) guidance. Moreover, with the multiple satellite-to-aircraft and ground-to-aircraft links required and the myriad of airborne GPS computations and corrections necessary, a heavy burden is placed on the equipment and processing in the aircraft, and not in the ground station where it should be.
D. Any satellite system is subject to jamming, either intentional or unintentional, and the complete dependence on GPS for global navigation, surveillance, landing guidance and other aviation functions has a tendency to lead to disaster.
In papers presented to the Institute of Navigation convention on Jun. 28, 1984 and Jun. 4, 1994, the present inventor described a new type of global surveillance and navigation system, which he designated an Integrated Global Surveillance and Navigation System (IGSANS). This system overcomes the drawbacks of the prior art GPS and GNSS-type systems, including those discussed in the preceding paragraphs.
The Integrated Global Surveillance and Navigation System (IGSANS) to be described herein consists of a satellite constellation and associated ground stations (satellite subsystem), and a ground station network (ground subsystem), each providing aircraft position data to an airborne subsystem. The basic functions provided by the IGSANS to be described are as follows: (a) precise global three-dimensional aircraft position for ATC surveillance; (b) precise global area navigation, pilot-selectable or standard routes, including great circle; (c) precise three-dimensional aircraft positions available globally to all aircraft in an area for collision warning/avoidance, and one which permits horizontal as well as vertical escapes; (d) a high speed two-way data link for aircraft requests, instructions, weather/runway conditions, etc.; and (e) in terminal areas, precise and versatile multi-runway landing guidance capabilities, including auto-flare guidance to touchdown and roll-out for all aircraft, with a high degree of freedom from multi-path errors.
It may be seen from the character of the IGSANS functions that aircraft position determination and data linking are at the heart of the system. Position determination via the satellite subsystem is accomplished with measurement of distances between the aircraft and three or more satellites of known position. The area satellite subsystem ground station transmits a digitally encoded and discretely addressed interrogation pulse concerning a particular aircraft to a satellite which, in turn, repeats the pulse to the addressed aircraft. The aircraft's digitally encoded reply pulse is received by three or more satellites, which again repeat the pulses to the satellite ground station. Precise time delay measurements between the interrogation and reply pulses allow the ground station to compute the precise aircraft position. In the case of the ground subsystem a facility in the vicinity of the aircraft transmits a similar discretely-addressed interrogation pulse to the aircraft. The time delay for the aircraft reply is measured to determine distance, and the incident angle of the reply signal wave front is measured by an interferometer antenna array to determine the precise azimuth angle.
The present invention provides an improved Integrated Global Surveillance and Navigation System (IGSANS) which is constructed to meet all the requirements of global ATC surveillance, navigation and collision warning/avoidance, precise landing guidance and high speed data link functions. The improved system provides a combined ground/satellite based system which results in substantial cost savings in both airborne and ground/satellite facilities and yet achieves the desired results discussed above.
The specific objectives of the present invention include the following:
A. to provide an improved combination ground and satellite system which utilizes spread spectrum technology to provide precise global navigation, surveillance, collision avoidance, landing guidance and data link capabilities; PA1 B. to provide such an improved combination ground/satellite system which utilizes spread spectrum technology to identify specific ground network stations or specific satellite area beams; PA1 C. to provide such an improved combination ground/satellite system which utilizes spread spectrum technology to permit overlaying and operating of the system in an existing band of narrow band channels with minimal mutual interference; PA1 D. to provide such an improved system having ground facilities which utilize interferometer angular measurements and spread spectrum technology to identify the facility and provide precise three-dimensional position measurements for landing guidance; and PA1 E. to provide such an improved system having airborne transponder equipment which communicates with ground/satellite subsystems utilizing spread spectrum technology to provide precise aircraft navigation, surveillance, collision avoidance, landing guidance and data link capabilities.